2,215 research outputs found
Analysis of a Waveguide-Fed Metasurface Antenna
The metasurface concept has emerged as an advantageous reconfigurable antenna
architecture for beam forming and wavefront shaping, with applications that
include satellite and terrestrial communications, radar, imaging, and wireless
power transfer. The metasurface antenna consists of an array of metamaterial
elements distributed over an electrically large structure, each subwavelength
in dimension and with subwavelength separation between elements. In the antenna
configuration we consider here, the metasurface is excited by the fields from
an attached waveguide. Each metamaterial element can be modeled as a
polarizable dipole that couples the waveguide mode to radiation modes. Distinct
from the phased array and electronically scanned antenna (ESA) architectures, a
dynamic metasurface antenna does not require active phase shifters and
amplifiers, but rather achieves reconfigurability by shifting the resonance
frequency of each individual metamaterial element. Here we derive the basic
properties of a one-dimensional waveguide-fed metasurface antenna in the
approximation that the metamaterial elements do not perturb the waveguide mode
and are non-interacting. We derive analytical approximations for the array
factors of the 1D antenna, including the effective polarizabilities needed for
amplitude-only, phase-only, and binary constraints. Using full-wave numerical
simulations, we confirm the analysis, modeling waveguides with slots or
complementary metamaterial elements patterned into one of the surfaces.Comment: Original manuscript as submitted to Physical Review Applied (2017).
14 pages, 14 figure
MEMS-reconfigurable metamaterials and antenna applications
This paper reviews some of our contributions to reconfigurable metamaterials,
where dynamic control is enabled by micro-electro-mechanical systems (MEMS)
technology. First, we show reconfigurable composite right/left handed
transmission lines (CRLH-TLs) having state of the art phase velocity variation
and loss, thereby enabling efficient reconfigurable phase shifters and
leaky-wave antennas (LWA). Second, we present very low loss metasurface designs
with reconfigurable reflection properties, applicable in reflectarrays and
partially reflective surface (PRS) antennas. All the presented devices have
been fabricated and experimentally validated. They operate in X- and Ku-bands.Comment: 8 pages; 8 figures; International Journal of Antennas and Propagatio
Physical modeling and validation of porpoises' directional emission via hybrid metamaterials
© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dong, E., Zhang, Y., Song, Z., Zhang, T., Cai, C., & Fang, N. X. Physical modeling and validation of porpoises' directional emission via hybrid metamaterials. National Science Review, 6(5), (2019): 921-928, doi:10.1093/nsr/nwz085.In wave physics and engineering, directional emission sets a fundamental limitation on conventional simple sources as their sizes should be sufficiently larger than their wavelength. Artificial metamaterial and animal biosonar both show potential in overcoming this limitation. Existing metamaterials arranged in periodic microstructures face great challenges in realizing complex and multiphase biosonar structures. Here, we proposed a physical directional emission model to bridge the gap between porpoises’ biosonar and artificial metamaterial. Inspired by the anatomical and physical properties of the porpoise's biosonar transmission system, we fabricated a hybrid metamaterial system composed of multiple composite structures. We validated that the hybrid metamaterial significantly increased directivity and main lobe energy over a broad bandwidth both numerically and experimentally. The device displayed efficiency in detecting underwater target and suppressing false target jamming. The metamaterial-based physical model may be helpful to achieve the physical mechanisms of porpoise biosonar detection and has diverse applications in underwater acoustic sensing, ultrasound scanning, and medical ultrasonography.E.D., Y.Z., Z.S., T.Z. and C.C. acknowledge the financial support in part by the National Key Research and Development Program of China (2018YFC1407504), the National Natural Science Foundation of China (41676023, 41276040 and 41422604). N.X.F. acknowledges the support from the MIT Energy Initiative grant. Z.S. thanks the China Scholarship Council for the financial support of his oversea study in Woods Hole Oceanographic Institution
Octave-spanning broadband absorption of terahertz light using metasurface fractal-cross absorbers
Synthetic fractals inherently carry spatially encoded frequency
information that renders them as an ideal candidate for broadband optical structures.
Nowhere is this more true than in the terahertz (THz) band where there is a lack of
naturally occurring materials with valuable optical properties. One example are perfect
absorbers that are a direct step toward the development of highly sought after detectors
and sensing devices. Metasurface absorbers that can be used to substitute for natural
materials suffer from poor broadband performance, while those with high absorption
and broadband capability typically involve complex fabrication and design and are
multilayered. Here, we demonstrate a polarization-insensitive ultrathin (∼λ/6) planar
metasurface THz absorber composed of supercells of fractal crosses capable of spanning
one optical octave in bandwidth, while still being highly efficient. A sufficiently thick
polyimide interlayer produces a unique absorption mechanism based on Salisbury
screen and antireflection responses, which lends to the broadband operation.
Experimental peak absorption exceeds 93%, while the average absorption is 83% from 2.82 THz to 5.15 THz. This new
ultrathin device architecture, achieving an absorption-bandwidth of one optical octave, demonstrates a major advance toward a
synthetic metasurface blackbody absorber in the THz ban
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